1. Field of the Invention
The present invention relates to a process for preparing particular 2,2-difluoroethylamine derivatives proceeding from 2,2-difluoroethyl-1-haloethane.
2. Description of Related Art
2,2-Difluoroethylamine derivatives are useful intermediates in the preparation of active agrochemical ingredients (see WO 2007/115644). Various processes are known for preparation of 2,2-difluoroethylamine derivatives.
WO 2009/036900 describes, for example, a process for preparing 2,2-difluoroethylamine derivatives by amide hydrogenation of N-[(6-chloropyridine-3-yl)methyl]-2,2-difluoroacetamide (Scheme 1).

A disadvantage of this process is the use of complex hydrides such as sodium borohydride, because hydrides are expensive and the use thereof requires complex safety measures.
WO 2009/036901 describes the reduction of N-(6-chloropyridin-3-yl)methylene-2,2-difluoroethanamine by hydrogen (Scheme 2).

A disadvantage of this process is the use of hydrogen because, here too, the use of hydrogen requires very complex safety measures.
Publication WO 2007/115644, which addresses the preparation of insecticidally active 4-aminobut-2-enolide compounds, describes the preparation of compounds of the general formula A-CH2—NH—R1 in which A represents specific heterocycles and R1 represents haloalkyl, by alkylating the nitrogen (Scheme 3).

Specifically, WO 2007/115644 describes the preparation of N-[(6-chloropyridin-3-yl)methyl]-2,2-difluoroethan-1-amine (compound (3)), which is synthesized proceeding from 2-chloro-5-chloromethylpyridine (compound (2)) and 2,2-difluoroethan-1-amine (compound (1)) in the presence of triethylamine (see Scheme 4). Compounds (1), (2) and triethylamine are used in equimolar amounts. The desired product is obtained in a yield of 53%.

WO 2007/115644 further states that the compounds N-[(6-chloropyridin-3-yl)methyl]-3-fluoropropan-1-amine, and N-[(6-chloropyridin-3-yl)methyl]-2-chloro-2-fluoroethan-1-amine were prepared in the same way.
The process described in WO 2007/115644 for preparation of compounds of the formula A-CH2—NH—R1, in which A represents specific heterocycles and R1 represents haloalkyl is disadvantageous since the nitrogen can be polyalkylated during the reaction. This leads to a yield loss, which is also evident from the yield of the specified example. The yield is only 53%. These polyalkylations can be reduced only by the use of a large excess of amine. Apart from the fact that amines are often very costly, the process is also therefore uneconomic since the amine which has been added in excess and not converted either has to be disposed of or recovered in a complex manner.
Due to the importance of 2,2-difluoroethylamine derivatives as units for synthesis of active agrochemical ingredients, it is, however, necessary to find a process which can be used on the industrial scale and inexpensively. It is also desirable to obtain specific 2,2-difluoroethylamine derivatives with high yield and high purity, such that the target compound preferably need not be subjected to any further, possibly complex purification. However, the abovementioned processes are unsuitable for this purpose.